Electrostatic coalescer with resonance tracking circuit

ABSTRACT

An electrostatic coalescer includes an outer wall defining a flow path for receiving a process fluid. A plurality of electrode plates is disposed within the flow path. A controller includes an inductor and a signal generator. The inductor is coupled in parallel with the plurality of electrode plates. The inductor and the plurality of electrode plates define a resonant circuit. The signal generator is coupled to the plurality of electrode plates and operable to apply an alternating current signal to the plurality of electrode plates at a frequency corresponding to a resonant frequency of the resonant circuit in the presence of the process fluid. The signal generator varies the frequency of the alternating current signal based on a positive feedback signal received from the resonant circuit to maintain resonance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/US2009/063392, filed Nov. 5, 2009,which claimed benefit of U.S. provisional patent application Ser. No.61/111,444, filed Nov. 5, 2008.

BACKGROUND

The disclosed subject matter relates generally to separating fluids in aprocess stream and, more particularly, to an electrostatic coalescerwith a resonance tracking circuit.

The separation of water from a hydrocarbon liquid is an importantprocess in the oil production industry. In an oil dominated regime,small water droplets can occur in the continuous oil phase due toshearing in upstream piping, for example. The droplet size is animportant contributing factor to the speed of the separation. Smalldroplets of water in oil separate slowly from the oil compared to largerdroplets due to the immiscibility of the liquids and the differences inspecific mass.

One conventional approach for oil/water separation makes use of gravityand requires large residence times inside separators. Large residencetimes are needed for an acceptable separation performance, and thereforethis approach is not suitable for an in-line application with high flowrates. Other techniques that use chemicals to break the emulsionsrequire later removal of the chemicals, thereby increasing cost. Stillother techniques that employ heating are less effective at breakingemulsions.

The separation of liquids from fluid streams that are primarily gas isalso an important process in industry. In many cases, gases with a higheconomical value are obtained containing very fine droplets of liquids.Examples may be natural gas or many other gases used in the chemicalindustry, such as chlorine or sulfur dioxide. Also, in process industry,vapors may partly condense, which may also result in gas containing fineliquid droplets, especially in high gas speed applications (i.e., thehigh speeds provide significant force to draw the droplets along).Further, any obstacle in the flow path may generate high and lowpressure areas, resulting in more condensation at the obstacle thancompared to low gas speed application, where the pressure differencesare much lower.

As these droplets can corrode piping and are harmful for pumps and otherprocessing equipment, they should be removed before packing ortransporting the commercial gas or using the gas in a process industry.Further, consumers want their products as pure as possible, andextraneous liquids lower the quality of these gases. In thepetrochemical industry, especially off shore, where natural gas isobtained together with salt water and oil, it is beneficial to removethe water and/or other liquids as near to the well as possible. Asignificant effort is spent drying the natural gas to remove water vaporto concentrations far below saturation with water absorbers. However,such efforts may be inefficient if the gas to be dried contains liquidwater in addition to vapors.

Conventional techniques for removing liquids from gases typically aim atimproving the traditional separation of liquids from gases by usinggravitation-like forces. One very old technique is based on theobservation that a piece of cloth hanging in a fog will collect waterfrom the fog, thus decreasing the fog intensity and providing water. Thecloth acts as a condensation center for the droplets and gravitationwill, in the case of water, cause excess water to flow down. Thistechnique is the basis for the separation of liquids from gases using amesh wire.

Another technology involves increasing the gravitational forces to makethe suspension of liquid droplets more instable in the gas.Gravitational forces can be increased by spinning the medium, whichresults in a centripetal force of many times normal gravitation. In thismanner, the separation proceeds at a rate many times faster than undergravitation alone, resulting in a much smaller apparatus.

Still, for large scale in-line operation both mesh wire technologies andaccelerators have their disadvantages. A mesh can become clogged andrequires the gas molecules to follow complicated paths through the mesh,costing mechanical energy. Increasing gravitational forces by spinningalso requires mechanical energy that is generally drawn from the gas tobe separated. This consumed mechanical energy results in a pressuredrop, which increases the required number or size of the pumps. Further,both techniques require sensitive equipment that is vulnerable toerosion.

This section of this document is intended to introduce various aspectsof art that may be related to various aspects of the disclosed subjectmatter described and/or claimed below. This section provides backgroundinformation to facilitate a better understanding of the various aspectsof the disclosed subject matter. It should be understood that thestatements in this section of this document are to be read in thislight, and not as admissions of prior art. The disclosed subject matteris directed to overcoming, or at least reducing the effects of, one ormore of the problems set forth above.

BRIEF SUMMARY

The following presents a simplified summary of the disclosed subjectmatter in order to provide a basic understanding of some aspects of thedisclosed subject matter. This summary is not an exhaustive overview ofthe disclosed subject matter. It is not intended to identify key orcritical elements of the disclosed subject matter or to delineate thescope of the disclosed subject matter. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

One aspect of the disclosed subject matter is seen in an electrostaticcoalescer. The electrostatic coalescer includes an outer wall defining aflow path for receiving a process fluid. A plurality of electrode platesis disposed within the flow path. A controller includes an inductor anda signal generator. The inductor is coupled in parallel with theplurality of electrode plates. The inductor and the plurality ofelectrode plates define a resonant circuit. The signal generator iscoupled to the plurality of electrode plates and operable to apply analternating current signal to the plurality of electrode plates at afrequency corresponding to a resonant frequency of the resonant circuitin the presence of the process fluid.

Another aspect of the disclosed subject matter is seen a method forcoalescing a disperse phase component in a process fluid. A flow pathfor receiving the process fluid is provided. A plurality of electrodeplates is disposed within the flow path. An inductor is coupled inparallel with the plurality of electrode plates. The inductor and theplurality of electrode plates define a resonant circuit. An alternatingcurrent signal is applied to the plurality of electrode plates at afrequency corresponding to a resonant frequency of the resonant circuitin the presence of the process fluid.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosed subject matter will hereafter be described with referenceto the accompanying drawings, wherein like reference numerals denotelike elements, and:

FIG. 1 is a simplified diagram of a fluid separation system inaccordance with one illustrative embodiment of the present subjectmatter;

FIG. 2 is a simplified cross-section view of an electrostatic coalescerin the system of FIG. 1;

FIG. 3 is a diagram of a flow disrupting element that may be used in theelectrostatic coalescer of FIG. 2;

FIG. 4 is a simplified block diagram of a control circuit of theelectrostatic coalescer of FIG. 1;

FIG. 5 is a simplified diagram of a positive loop that may be employedin an AC generator in the control circuit of FIG. 4;

FIG. 6 is a simplified block diagram of an autogenerator circuit thatmay be employed in the control circuit of FIGS. 4 and 5;

FIG. 7 is a simplified block diagram of an alternative embodiment of acontrol circuit of the electrostatic coalescer of FIG. 1;

FIG. 8 is a simplified block diagram of a fluid separation systemincorporating an external energy source with an electrostatic coalescer;

FIGS. 9 and 10 are cross-section views of an alternative embodiment ofan electrostatic coalescer with intermediate insulating members disposedbetween electrode plates; and

FIGS. 11 and 12 are cross-section views of an electrostatic coalescer inaccordance with another illustrative embodiment of the presentinvention.

While the disclosed subject matter is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the disclosed subjectmatter to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosed subject matter asdefined by the appended claims.

DETAILED DESCRIPTION

One or more specific embodiments of the disclosed subject matter will bedescribed below. It is specifically intended that the disclosed subjectmatter not be limited to the embodiments and illustrations containedherein, but include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as come within the scope of the following claims. It shouldbe appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure. Nothing in thisapplication is considered critical or essential to the disclosed subjectmatter unless explicitly indicated as being “critical” or “essential.”

The disclosed subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the disclosed subject matter with details thatare well known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe disclosed subject matter. The words and phrases used herein shouldbe understood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

Referring now to the drawings wherein like reference numbers correspondto similar components throughout the several views and, specifically,referring to FIG. 1, the disclosed subject matter shall be described inthe context of a fluid separation system 10. The system 10 includes anelectrostatic coalescer 15 disposed upstream of a separator 20. Theelectrostatic coalescer 15 is resident in a fluid stream defined bypiping 25.

For purposes of the following discussion, a fluid stream may be aprimarily liquid stream or a primarily gas stream. In the illustratedembodiment, the electrostatic coalescer 15 is operable to increase thesize of liquid droplets in a process fluid, such as a hydrocarbon fluid.For example, the coalesced liquid may be water present in a liquidhydrocarbon stream or a gas stream (e.g., natural gas). Of course, theparticular fluid provided to the electrostatic coalescer 15 may vary,and fluids other than hydrocarbon fluids may be processed. The liquidcoalesced from the process fluid may also vary, with water being onlyone illustrative example. In another example, liquids may be separatedfrom the process gases (e.g., chlorine or HCl). Water droplet sizes inchlorine gas streams may be enlarged by the electrostatic coalescer 15to more effectively remove water from the chlorine, before dealing withthe gaseous water vapor.

The separator 20 operates to remove at least a portion of the liquidpresent in the process fluid and provides a process fluid outlet 30 anda coalesced liquid outlet 35. The construction and operation of theelectrostatic coalescer 15 is described in greater detail below withrespect to FIGS. 2 and 3. The application of the present subject matteris not limited to any particular embodiment of the separator 20.Exemplary separator types include horizontal/gravity separators andenhanced gravity separators (e.g., cyclone based separation technology).In some embodiments, the electrostatic coalescer 15 and the separator 20may be integrated into a single unit.

Estimations and experience of electro-coalescence in liquid-liquidsystems show that the necessary value of electrical field to producecoalescence in a liquid-gas system should be in the range 10³-10⁴ V/cm.Typical values of electrical fields, which cause auto electron emission(i.e., the only charging mechanism for the droplets by electrostaticfields) are in the range larger than 10⁷ V/cm, so the above electricalfield will not produce any charging of the droplets.

In cases where the fluid being processed by the electrostatic coalescer15 is primarily gas, it is possible to generate an electric field acrossa gas due to the fact that gases are good insulators. In such anelectric field, charged particles are attracted to one of the electrodeplates 45. Uncharged particles will be polarized, and due todipole-dipole interaction, an attractive force between them will appear,while they remain unattracted by the electrode plates 45. The forcesgenerated by the electrical field in the coalescer 15 are too weak toionize the free particles.

Although this description illustrates the separation of water from ahydrocarbon fluid, the electrostatic coalescer 15 may be applied toapplications with other emulsions where the specific resistance of thecontinuous phase is larger than about 10⁷ Ohm*m and where the electricpermeability of continuous and disperse phases are different. Forexample, the water droplet sizes in hydrocarbon gas streams may beenlarged by the electrostatic coalescer 15 to more effectively dry thegas. In general, more conductive emulsions may require higherfrequencies of the applied voltage.

In general, the electrostatic coalescer 15 is more effective in causingcoalescence when the water cut is at least about 2%. This amount mayvary depending on the particular process fluid and flow rate. In caseswhere the water cut of the process fluid is less than an efficientvalue, a water injection port 37 may be disposed upstream of theelectrostatic coalescer 15 to increase the water content of the processfluid prior to coalescence and separation.

FIG. 2 illustrates a cross-section view of the electrostatic coalescer15. In the illustrated embodiment, the diameter of an outer wall 40 ofthe electrostatic coalescer 15 roughly corresponds to the diameter ofthe piping 25 in which it is installed to provide an in-linearrangement. Fluid passing through the piping 25 passes through theelectrostatic coalescer 15 at substantially the same flow rate. Aplurality of electrode plates 45 are provided in the electrostaticcoalescer 15 through which the fluid travels. In some embodiments,obstructive elements 52 may be provided in the areas where no electricalfield is generated to ensure the exposure of all of the fluid to theelectrical fields.

The electrostatic field generated by the electrode plates 45 polarizesliquid droplets in the process stream to locally neutralize theelectrostatic field. The polarized droplets are not attracted by thehomogeneous field to one of the electrodes 45 because the net charge ofthe droplet is zero. The polarized droplets do feel the gradient of theelectrostatic field at short range of other droplets. In this manner,the droplets are attracted to one another.

The particular geometry of the electrode plates 45 (e.g., arrangement,number, thickness, etc.) may vary depending on factors associated withthe particular implementation, such as process fluid, piping diameter,fluid pressure, expected flow rate, etc. For example, the spacing of theelectrode plates 45 may vary depending on the processed fluid. Theelectrode plates 45 in a gas coalescer may be spaced more closelytogether than in a liquid coalescer. This reduced spacing may beachieved by reducing the diameter of the coalescer 15 as compared tothat of the piping 25 to allow the same number of electrode plates 45 tobe used, but spaced more closely. Alternatively, the diameter may not bereduced, but the number of electrode plates 45 may be increased. In someapplications, long electrode plates 45 having a length several times thediameter of the electrostatic coalescer 15 may be used to increase theresidence time or to lower the required field strength.

As illustrated in FIG. 2, the inside surface of the outer wall 40 andthe electrode plates 45 are coated with a protective layer 50.Generally, the protective layer 50 protects the electrode plates 45 fromerosive or corrosive effects of the process fluid (e.g., due toparticles or chemicals in the process fluid) and may also serve as anelectrical insulator to reduce the likelihood of arcing between adjacentelectrode plates 45. Exemplary materials for the protective layer 50include epoxy, electrically non-conducting ceramics, plastic coatings,etc. formed using processes such as molding, chemical vapor deposition,physical vapor deposition sintering, etc. Alternatively, electricallyinsulating layers may be combined with other protective layers on theoutside surfaces to meet the mechanical requirements of the application(e.g., abrasion resistance or corrosion resistance). For example, aninsulating epoxy coating may be covered by a ceramic conducting coating.The particular insulator and/or abrasion resistant coating selected mayvary depending on mechanical requirements, cost, and material electricalproperties (e.g., dielectric constant).

The electrode plates 45 may be sized and arranged to provide for arelatively high Reynolds number, thereby providing turbulent flow of theprocess fluid through the electrostatic coalescer 15. Turbulent flowcauses the velocity of the process fluid to vary in a random manner,causing an increase in the small-scale movements of the fluid. Thisincrease in movement makes it more likely that water droplets in theprocess stream will come in close proximity with one another. At thisclose proximity, the dipolar interaction induced by the electrostaticfield described above will be stronger, thereby increasing coalescence.

In one embodiment illustrated in FIG. 3, one or more flow disruptingelements 52 may be provided in the electrostatic coalescer 15 to enhancemicroturbulence between the electrode plates 45. The flow disruptingelement 52 may be fabricated from an electrically insulative material,such as a ceramic, plastic, or other electrically-non-conductive solidmaterial. The flow disrupting element 52 includes a plurality of pillars53 interconnected by cross members 54 in a grid arrangement. The griddisrupts the flow of process fluid through the electrostatic coalescer15 to increase turbulence. The flow disrupting element 52 may bepositioned between adjacent electrode plates 45. The sizing of the flowdisrupting element 52 may vary depending on the particular arrangementand sizing of the electrode plates 45. Flow disrupting elements 52 maynot be required in implementations where the flow rate and Reynoldsnumber are sufficiently high to provide turbulent flow.

In an application where the fluid stream exhibits a high degree oflaminar flow, the central part of the stream will have a much higherspeed than the part along the walls. This flow characteristic may resultin a short residence time between the electrode plates 45 In addition toor in place of the flow disrupting elements 52 to induce turbulence,flow guides may be provided to make the distribution of flow over theelectrode plates 45 more even in terms of kg/hour, resulting in a betteruse of the electrostatic coalescer 15.

Referring to FIG. 4, a simplified block diagram of a control circuit 55of the electrostatic coalescer 15 is provided. The properties of theprocess fluid affect the net electrical characteristics of theelectrostatic coalescer 15. Hence, the electrostatic coalescer 15 ismodeled as a capacitor 60 in parallel with a resistor 62 representingthe net capacitance and resistance defined by the arrangement of theelectrode plates 45 and the process fluid passing through them. Thecontrol circuit 55 includes an inductor 64 and an alternating current(AC) generator 66. Collectively, the inductor 64 and the capacitor 60and resistor 62 that model the electrostatic coalescer 15 and processfluid define a resonant circuit 68. In general, the AC generator 66maintains its output frequency at the resonant frequency of the resonantcircuit 68 to minimize the current needed to drive the electrostaticcoalescer 15. The AC generator 66 generates a variable frequencysinusoidal waveform that is applied to the electrode plates 45 to fostercoalescence in the process fluid.

In one embodiment, the AC generator 66 may be an autogenerator circuit.As known to those of ordinary skill in the art, an autogenerator isgenerally an amplifier with large amplification having an exit connectedto the entrance, commonly referred to as a positive loop. The positiveloop includes a resonant circuit that defines the frequency ofoscillation. In this embodiment, the resonant circuit 68 is coupled tothe positive loop of the AC generator 66, thereby providing for passivefrequency adjustment of the AC generator 66 corresponding to theresonant frequency of the resonant circuit 68. FIG. 5 illustrates howthe resonant circuit 68 is incorporated into the positive loop of the ACgenerator 66 through a comparator 85. Because of the positive feedback,the AC generator 66 operates at the resonant frequency of the resonantcircuit 68. Because the inductor 64 is fixed, the frequency adjustsaccording to the varying properties of the process fluid and theresulting capacitance of the electrostatic coalescer 15. As theproperties of the fluid change over time, the AC generator 66automatically maintains its output at the varying resonant frequency,thereby minimizing the current requirements required for driving theelectrostatic coalescer 15.

FIG. 6 is a simplified block diagram of the autogenerator circuit thatmay be employed for the AC generator 66. The autogenerator circuitincludes a power unit 70 that receives an AC input voltage (e.g., 220V,50 Hz) and generates DC output voltages (e.g., +300V, +50V, +12V, +9V,etc.) for powering the other units of the circuit. A driving generator72 produces driving pulses at double frequency. A signal conditioner 74produces signals for a frequency phase adjustment unit 76 and forswitching the gates of transistors in a power amplifier 78. The poweramplifier 78 is a push-pull amplifier. The frequency phase adjustmentunit 76 compares the phases of the driving generator 72 and an outputsignal and adjusts the frequency of the driving generator 72 to achieveresonance with varying load characteristics. A resonance transformer 80forms a sinusoidal output signal with an amplitude up to 3 kV, forexample for powering the electrostatic coalescer 15. A positive feedbackpath exists between the resonance transformer 80 and the frequency phaseadjustment unit 76.

A control unit 82 controls the frequency and amplitude of the outputsignal, and in response to a condition that exceeds defined limits, setsthe AC generator 66 into a safe mode (i.e., low power). An indicatorunit 84 indicates the parameters of the output signal. An interface 86may be provided for connecting the AC generator 66 to an externalcomputing device 88, such as a personal computer, controller, or someother general purpose or special purpose computing device for allowingtracking of device parameters, such as frequency, amplitude and consumedpower, or to allow operator intervention or system configuration.

FIG. 7 illustrates an alternate embodiment of a control circuit 90,where an AC generator 95 is a signal generator that outputs aconfigurable frequency signal. For example, the AC generator 95 may be avoltage controlled oscillator. The voltage at a resistor 100 representsa measure of the output current of the control circuit 90 for drivingthe electrostatic coalescer 15. The AC generator 95 measures the outputcurrent and automatically adjusts its output frequency to minimize thevalue of the measured voltage, which corresponds to a resonancecondition. Hence, the AC generator 95 actively adjusts its outputfrequency based on the measured drive current to obtain the resonantfrequency of the resonant circuit 68.

Generally, the frequency of the oscillation is above 1 kHz due to therelaxation time associated with most types of crude oil, which is in therange of 0.02-0.003 seconds. In the illustrated embodiment, it isassumed that the capacitance is about 0.1 μF and the nominal frequencyis about 10 kHz, which provides for and inductance of about 3 mH. Ofcourse, the inductor 64 may be sized differently based on differentassumptions about the process fluid and geometry of the electrostaticcoalescer 15. The Q value corresponding to the resonance condition thatresults in the diminishing of the drive current is given by:Q=2ωL/R

Monitoring the frequency of the control circuit 55, 90 providesinformation regarding the capacitance of the coalescer 15, and thereforethe water cut. The power consumption of the electrostatic coalescer 15is defined by the resistance of the process fluid. The electricalresistance of the process fluid and the value of the water cutcharacterize the quality of the process fluid being processed. Theresistance can provide information regarding the salinity of the processfluid. The water cut of the process fluid entering the electrostaticcoalescer 15 effectively defines the final water cut after the separator20. Hence, by utilizing the water cut and the resistance information,diagnostic tools may be defined to characterize the process fluid.

In some embodiments, the efficiency of the coalescence may be enhancedby providing an external energy source that operates in conjunction withthe electrostatic coalescer 15. As shown in FIG. 8, an energy source 105may be coupled to the electrostatic coalescer 15. Exemplary energysources include microwave or ultrasound devices. Exposing the processfluid to a microwave or ultrasonic energy field may increase thecoalescence provided by the electrostatic coalescer 15. The need for anexternal energy source 105 may depend on characteristics such as thesize of the electrostatic coalescer 15, the characteristics of theprocess fluid, the flow rate, etc. Information gathered from theresonant frequency of the resonant circuit 68, which defines thecharacteristics of the process fluid, may be used to tune the externalenergy source 105. For example, experiments may be conducted to identifythe optimal frequency or amplitude characteristics of the microwave orultrasound signals based on the characteristics of the process fluid. Acorrelation between the determined resonant frequency and the externalenergy source characteristics may then be determined to increase theeffectiveness of the external energy source 105.

In another embodiment illustrated in FIG. 9, an electrostatic coalescer110 may be provided with an intermediate insulating member 115 disposedbetween the electrode plates 120A, 120B to define a first flow pathbetween the insulating member 115 and the first electrode plate 120A anda second flow path between the insulating member 115 and the secondelectrode plate 120B. One or more insulating members 115 may be disposedbetween the pair of electrode plates 120A, 120B to define additionalflow paths therebetween (e.g. a third flow path between adjacentinsulating members 115). Although only two electrode plates 120A, 120Bare illustrated, different configurations may be used, including thearrangement shown in FIG. 2, where parallel plate electrodes are used.In such a case one or more insulating members 115 may be disposedbetween each pair of electrode plates 45. Of course other geometries mayalso be used.

For purposes of illustration, the electrode plate 120A is grounded, andthe electrode plate 120B is coupled to a power source 125, such as oneof the power sources 66, 95 described above, or a different powersource. Typically, the electrode 120B is coated with a protective layer130 to protect the electrode plate 120B from erosive or corrosiveeffects of the process fluid (e.g., due to particles or chemicals in theprocess fluid). The protective layer 130 may also serve as an electricalinsulator to reduce the likelihood of arcing. The grounded electrodeplate 120A may or may not have a protective layer 130. The resonantcircuit 68 described above may or may not be implemented in theelectrostatic coalescer 110.

The insulating member 115 disposed between the two electrode plates120A, 120B increases coalescence efficiency. Coalescence of droplets inanother medium relies on the polarization of conducting liquid particlesin an electrical field. Due to the required high field, and thepreference not to use very high voltages, the electrodes are normallydisposed in close proximity to one another. Under normal circumstances,water droplets that happen to be in-line with the electrical field, willbe aligned in a “chain” of water droplets that do not coalescenceeffectively because the attraction to a droplet in the middle of thechain to one side will be equal to that to the other side, negating theattraction, while the droplets on the electrode will not release. Onlydroplets on free ends will move and, thereby, coalesce. This chain ofdroplets reduces the field strength, and therefore the coalescence,which reduces the efficiency of the coalescence. In some cases, wherehigh field and long chains are present, sparking can occur. The higherthe water concentration, the more droplets are present, and thereforethe higher the influence of this effect. The insulating member 115 tendsto break up these chains or even prevent them from forming, resulting ina higher coalescence efficiency.

The insulating member 115 may be hydrophilic (i.e., water attracting) orhydrophobic (i.e., water repelling). The attractive forces between waterand a hydrophilic surface are relatively small compared to those foundin electric fields. The dielectric constant of the material used for theinsulating member 115 may vary depending on the particularimplementation. If an insulator with high dielectric constant (i.e.,higher than the surrounding medium) is used, the influence the dropletsexperience from each other, even assuming contact between the dropletsand the surface of the insulator, will be smaller than the thicknesswould predict. Therefore, in situations where not much space is presentbetween electrodes 120A, 120B, a thin, high dielectric constantinsulator may be used. On the other hand, due to mechanicalrequirements, the insulating member 115 may, in some cases, be ratherthick, which would result in a preference for an insulator with a lowdielectric constant. Where a material with a high dielectric constant iscombined with one with a low constant in an electrical field, theelectrical field strength will concentrate in the high dielectricconstant material. A lower dielectric constant material for theinsulating member 115 will support the goal of building the electricalfield over the medium to be coalesced by reducing the fields in theinsulating member 115, thereby allowing a smaller applied voltage andresulting in safer operations with less power consumption.

Providing multiple insulating members 115 between the electrode plates120A, 120, as shown in FIG. 10, tends to further increase the efficiencyof the coalescence. The region between the insulating members 115 willbe free of water droplet chains, which were found to reduce efficiency.By placing the insulating members 115 close to the electrodes 120A, 120B(i.e., without merging with them, which would reduce the insulatorfunction), a higher efficiency can be obtained.

In contrast to electro coalescence of water in water-in-oil systems, theconductivity of gases is far less than the conductivity of crude oils.This circumstance makes it possible to use a DC voltage power source tocreate an electrical field in the gas media. In some applications, theelectrostatic coalescer 15 may be employed in a gas application and acontrolled resonance AC power source may be used.

FIG. 11 illustrates an alternative embodiment of an electrostaticcoalescer 150 that may be employed in an application where the processfluid is primarily gas. The electrostatic coalescer 150 includes anouter wall 155 and external electrodes 160 coupled to a power source162. The outer wall may be an electrically insulating material. Anenclosure 170 may be provided around the external electrodes 160 forprotective purposes. In the illustrated embodiment, the power source 162is a DC power source, however, an AC source may also be used. The use ofthe external electrodes 160 allows the electrical field to be generatedwhile minimizing the obstruction of the flow.

In yet another embodiment shown in FIG. 12, the electrostatic coalescer150 described in reference to FIG. 11 may be provided with one or moreelectrically conductive members 175 disposed between the externalelectrodes 160 to increase the electrical field strength. The conductivemembers 175 are not connected to any power source, so they do notoperate as electrodes. The conductive members 175 may be coated toprovide the required characteristics, as described above in relation tothe electrode plates 45. Interposed conductive members 175 may also beused in the embodiment illustrated in FIG. 2.

Although the electrostatic coalescers 15, 110, 150 are illustrated anddescribed herein as being in-line devices, it is contemplated that thetechniques described herein may be applied to other types of coalescers,such as vessel based coalescers.

The use of an electrostatic force to coalesce liquid droplets in a fluidflow allows more efficient downstream removal of the droplets, therebyreducing the demands on the removal equipment and lowering its cost orincreasing the amount of liquid that can be removed, thereby providing ahigher purity processed fluid.

The particular embodiments disclosed above are illustrative only, as thedisclosed subject matter may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of thedisclosed subject matter. Accordingly, the protection sought herein isas set forth in the claims below.

We claim:
 1. An electrostatic coalescer, comprising: an outer walldefining a flow path adapted to receive a process fluid comprised of ahydrocarbon-containing fluid and water droplets; a plurality ofelectrode plates disposed within said flow path; and a controller,comprising: an inductor coupled in parallel with said plurality ofelectrode plates, said inductor, said plurality of electrode plates andsaid process fluid, when present, between said electrode plates,defining a resonant circuit; and a signal generator coupled to saidplurality of electrode plates and operable to apply an alternatingcurrent signal to said plurality of electrode plates at a frequencycorresponding to a resonant frequency of said resonant circuit in thepresence of said process fluid, wherein said signal generator is adaptedto automatically vary the frequency of said alternating current signalbased upon varying properties of said process fluid so as to maintainresonance and thereby facilitate coalescence of at least some of thewater droplets in the process fluid.
 2. The electrostatic coalescer ofclaim 1, wherein said resonant circuit is further adapted to provide apositive feedback signal to said signal generator based upon saidvarying properties of said process fluid.
 3. The electrostatic coalescerof claim 1, wherein said varying properties of said process fluid iscomprised of at least one of an electrical resistance of said processfluid, a salinity of said process fluid or a water cut of said processfluid.
 4. The electrostatic coalescer of claim 1, wherein said signalgenerator further comprises a positive loop input that is coupled tosaid resonant circuit.
 5. The electrostatic coalescer of claim 1,wherein said outer wall defines a pipe having a circular cross-section.6. The electrostatic coalescer of claim 1, wherein said plurality ofelectrode plates comprise parallel linear plates.
 7. The electrostaticcoalescer of claim 6, wherein at least a subset of said plurality ofelectrode plates is coated with an insulative material.
 8. Theelectrostatic coalescer of claim 1, further comprising at least one flowdisrupting element disposed between two adjacent electrode plates thatis adapted to cause, at least in part, the flow of said process fluidbetween said two adjacent electrode plates to be turbulent flow.
 9. Theelectrostatic coalescer of claim 1, further comprising an energy sourcecoupled to said outer wall that is adapted to generate an energy fieldin said flow path.
 10. The electrostatic coalescer of claim 9, whereinsaid energy source comprises at least one of an ultrasound waveformgenerator or a microwave waveform generator.
 11. The electrostaticcoalescer of claim 1, wherein said outer wall defines a vessel or apipe.
 12. The electrostatic coalescer of claim 1, further comprising atleast one insulating member disposed between at least two of saidplurality of electrode plates.
 13. The electrostatic coalescer of claim1, wherein said signal generator is adapted to automatically vary thefrequency of said alternating current signal based upon varyingproperties of said process fluid so as to maintain resonance underturbulent flow conditions.
 14. An electrostatic coalescer, comprising:an outer wall defining a flow path adapted to receive a process fluidcomprised of a hydrocarbon-containing fluid and water droplets; aplurality of electrode plates disposed within said flow path; and acontroller, comprising: an inductor coupled in parallel with saidplurality of electrode plates, said inductor, said plurality ofelectrode plates and said process fluid, when present, between saidelectrode plates, defining a resonant circuit; and a signal generatorcoupled to said plurality of electrode plates and operable to apply analternating current signal to said plurality of electrode plates at afrequency corresponding to a resonant frequency of said resonant circuitin the presence of said process fluid, wherein said signal generator isadapted to automatically vary the frequency of said alternating currentsignal based upon varying properties of said process fluid so as tomaintain resonance and thereby facilitate coalescence of at least someof the water droplets in the process fluid when said process fluid flowis a turbulent fluid flow, wherein said varying properties of saidprocess fluid are comprised of at least one of an electrical resistance,a salinity and a water cut of said process fluid.
 15. The electrostaticcoalescer of claim 14, wherein said resonant circuit is further adaptedto provide a positive feedback signal to said signal generator basedupon said varying properties of said process fluid.
 16. Theelectrostatic coalescer of claim 14, wherein said signal generatorfurther comprises a positive loop input that is coupled to said resonantcircuit.
 17. The electrostatic coalescer of claim 14, further comprisingat least one flow disrupting element disposed between two adjacentelectrode plates that is adapted to cause, at least in part, saidturbulent flow of said process fluid between said two adjacent electrodeplates.
 18. The electrostatic coalescer of claim 14, further comprisingan energy source coupled to said outer wall that is adapted to generatean energy field in said flow path.
 19. The electrostatic coalescer ofclaim 18, wherein said energy source comprises at least one of anultrasound waveform generator or a microwave waveform generator.
 20. Asystem, comprising: an electrostatic coalescer, comprising: an outerwall defining a flow path adapted to receive a process fluid comprisedof a hydrocarbon-containing fluid and water droplets; a plurality ofelectrode plates disposed within said flow path; and a controller,comprising: an inductor coupled in parallel with said plurality ofelectrode plates, said inductor, said plurality of electrode plates andsaid process fluid, when present, between said electrode plates,defining a resonant circuit; and a signal generator coupled to saidplurality of electrode plates and operable to apply an alternatingcurrent signal to said plurality of electrode plates at a frequencycorresponding to a resonant frequency of said resonant circuit in thepresence of said process fluid, wherein said signal generator is adaptedto automatically vary the frequency of said alternating current signalbased upon varying properties of said process fluid so as to maintainresonance and thereby facilitate coalescence of at least some of thewater droplets in the process fluid; and a separator in fluidcommunication with and positioned downstream of said electrostaticcoalescer, wherein said separator is adapted to separate a dispersephase component from said process fluid.
 21. The system of claim 20,further comprising: piping that is in fluid communication with andpositioned upstream of said electrostatic coalescer; and an injectionport disposed in said piping positioned upstream of said electrostaticcoalescer for injecting water into the process fluid.
 22. The system ofclaim 20, wherein said energy source comprises at least one of anultrasound waveform generator or a microwave waveform generator.
 23. Amethod for coalescing water droplets entrained in ahydrocarbon-containing process fluid, comprising: providing a flow pathfor receiving said process fluid with the entrained water droplets;disposing a plurality of electrode plates within said flow path;providing an inductor coupled in parallel with said plurality ofelectrode plates, said inductor, said plurality of electrode plates andprocess fluid passing through the electrode plates defining a resonantcircuit, wherein the resonant circuit has a varying resonant frequencythat varies based upon variations in properties of the process fluid;determining a resonant frequency of the resonant circuit as processfluid passes through the plurality of electrode plates; andautomatically applying an alternating current signal to said pluralityof electrode plates at a frequency corresponding to the determinedresonant frequency of said resonant circuit so as to thereby facilitatecoalescence of at least some of the water droplets in the process fluid.24. The method of claim 23, further comprising applying an energy fieldto said process fluid.
 25. The method of claim 24, wherein applying saidenergy field comprises applying at least one of an ultrasound energyfield or a microwave energy field.